Due to the presence of wind farms in cold areas it is sometimes necessary to implement a system and a method that is able to detect anomalies on the power generated curves caused by the formation of ice or frost on the turbine rotor blades and other main components.
Ice accumulation in wind turbines poses a major problem in cold climate areas that both reduces the output of produced energy and shortens the expected lifetime of major wind turbine components. Wind turbines may be affected by several types of ice such as frost, sub cooled rain, wet snow, rime etc.
It is furthermore a problem not only encountered in cold climates, but it may also occur under a myriad of different conditions. Icing can occur in coastal areas, mainly of higher latitudes, as well as in mountainous terrain. The major problem at mountainous areas or near the top of hills is the formation of ice when the base of a cloud is situated at a lower height or altitude than the wind turbine hub or nacelle. Such an event is referred to as in-cloud icing. Snow rain is another common form of ice formation. Both cases normally show cloudiness conditions in common. On the other side it has been demonstrated that no ice formation will appear when skies are clear.
Known standards, such as Norm ISO 12494, define several types of ice and their meteorological conditions for them to form. Empirical variables include wind speed and direction, temperature and duration of the in-cloud condition for the wind turbine. These systems typically use hygrometers that are based on the principle that water vapour inside the clouds is very close or higher than the saturating vapour pressure. This means that the relative humidity is generally higher than 95%. However, said systems are not entirely reliable. In coastal areas and in offshore wind farms values of relative humidity may be high at all times, even without the presence of any clouds.
One of said systems is described in the patent document U.S. Pat. No. 7,086,834. A method for detecting ice on a rotor blade includes monitoring meteorological conditions and monitoring physical characteristics of the wind turbine that may cause a mass imbalance between the rotor blades.
Yet another problem of known systems is encountered on the hydrometer itself. If the calibration is effected for a value of water vapour saturating pressure when said water is in liquid form, it may result that incorrect relative humidity readings are obtained when temperature is lower than 0° C.
It is thus an object of the present invention to propose a system and method capable of detecting cloudiness conditions in a wind farm without the disadvantages of the prior art and to add a signal into a control algorithm for wind formation detection in a precise manner.
It is yet another object of the present invention to propose an alternative system and method that is simple and reliable and does not pose calibration problems.